1. Field of the Invention
This invention generally relates to a linear motion guide assembly suitable for use in various apparatuses and machines having movable parts, and, in particular, to a small-sized linear motion guide assembly incorporating therein its drive unit.
2. Description of the Prior Art
As shown in FIG. 7, a typical prior art linear motion guide assembly includes an elongated bed A having a U-shaped cross section formed with a pair of guide grooves and a sliding table B which is slidably mounted on the bed A with a plurality of rolling members interposed therebetween. Thus, the sliding table B may move linearly along the longitudinal direction of the elongated bed A back and forth. Typically, a rack and pinion type drive unit (not shown) is provided for driving to move the sliding table A relative to the bed A. However, such a prior art drive unit is relatively large in size, so that the overall size of the linear motion guide assembly tends to be bulky. Moreover, since there is a backlash in the mesh between the rack and the pinion, the accuracy in positioning the sliding table B is rather limited. Furthermore, since a rack and pinion drive unit tends to move the sliding table B upward, the rolling members interposed between the bed A and the sliding table B tend to be forced against the upper edge sections of the guide grooves, which tends to increase the sliding resistance and the wear of both of the bed A and the rolling members.